Display devices, such as a plasma display panel (hereinafter referred to as a “PDP”) and a field emission display (hereinafter referred to as an “FED”), have been gaining attention as flat panel display devices that can achieve both an increase in screen size and reductions in thickness and weight.
These display devices each are provided with a pair of panels between which a luminescence excitation space is formed. This luminescence excitation space is a space corresponding to, for example, a discharge space in a PDP, filled with a discharge gas containing an inert gas as its main component, or a vacuum space in an FED, from which electron beam energy emitted from an electron source can be obtained without attenuating the energy, and this space is required to have a high gas-tightness.
The atmosphere in a luminescence excitation space needs to be adjusted when a display device is produced. The atmosphere is adjusted via a tube (a vent tube) mounted on a panel so as to be communicated with a hole (a vent hole) formed in the panel. As such a vent tube, a tube having a stable tip shape, for example, a tube having an enlarged diameter portion 53 and a flange portion 52, as shown as a tube 12 in FIG. 7A, commonly is used to improve its stability in bonding to the panel. The tube is mounted on the panel using a glass ring having a stepped portion, as a saucer for the opening portion at the tip of the tube to be fitted into the ring, formed on the surface of the inner peripheral wall thereof, as shown as a ring 22 in FIG. 7A. After the vent hole, the vent tube and a through-hole of the glass ring are aligned with one another, the glass ring is melted to form a glass member, so that the tube 12 is mounted on the panel 1b via the glass member 23 so as to cover the hole 11 formed in the panel 1b, as shown in FIG. 7B.
It is not easy to form a glass ring of a complex shape as shown in FIG. 7A without causing a defect such as a crack, a chip, and deterioration of glass, and therefore a glass material that can be used for such a glass ring is limited only to a lead oxide glass.
From the viewpoint of natural environmental protection, there is a need to replace a conventional lead glass with a lead-free glass, as a glass material. As a candidate for such a glass material, for example, JP2003-238199A and JP2004-182584A have proposed a glass material containing phosphorus oxide (P2O5) (phosphate glass material).
It is very difficult, however, to form, using a phosphate glass material, a glass ring not only having a complex shape corresponding to the stable tip shape of a vent tube but also having few defects such as a crack and deterioration.